1. Chapter 10 Properties of Solids and Liquids (Molecular Structures)
Learning Goal
Draw Lewis structures for molecular compounds or polyatomic ions.
Draw resonance structures for certain polyatomic ions.
Predict molecular structures of molecule and ions.
Use electronegativity to determine the polarity of a bond or a molecule.
Describe the attractive forces among molecules.
Describe the changes of state between solids, liquids, and gases; calculate the energy involved.

2. 10.1 Electron-Dot Symbols
Electron-dot symbols show single dots or pairs of dots on the sides of an atomic symbol

3. Electron-Dot Formulas (Lewis Structures)
Electron-dot formulas show
The sequence of bonded atoms in a molecule or polyatomic ion
The bonding pairs of electrons shared between atoms
The nonbonding or unshared (lone pairs) of electrons
The central atom bonded to other atoms
The electron-dot formula for H2O contains:
8 valence electrons (6 from O plus 1 from each hydrogen atom)
Two bonding pairs (between the H and O atoms) and two lone pairs (on the O atom)

4. The Octet Rule and the Bonding Trend in the Periodic Table
Octet Rule: each atom would like to attain 8 electrons in its valence shell. (noble gas configuration)

6. Bonding Trends in C, N, and O
C N O O-
In a single bond, one pair of electrons is shared.
In a double bond, two pairs of electrons are shared.
In a triple bond, three pairs of electrons are shared.

7. Exceptions to the Octet Rule
Exceptions to the octet rule include:
Hydrogen, H, only gets a single bond
Boron, B, has only 3 electrons around it to form bonds
BF3
Compounds of P, S, Cl, Br, and I can have expanded octets with 10, 12, or even14 valence electrons around them
SF4, SF6, PF5, ClO3-, ClO4-

8. Draw the Lewis Structure for: a. NF3
Learning Check
Draw the Lewis Structure for:
a. NF3
b. H2CO
F N F F .. : : ..
H C O H

9. Draw the electron-dot formula for PCl3
Draw the electron-dot formula for PCl3. P forms 3 bonds and Cl forms one bond.

10. Multiple Bonds, CO2
In carbon dioxide, CO2, octets are achieved by sharing two pairs of electrons between atoms; this is called a double bond.

11. Multiple Bonds, N2
In nitrogen, N2, octets are achieved by sharing three pairs of electrons between atoms; this is called a triple bond.

12. Multiple Bonds, O2
In oxygen, O2, octets are achieved by sharing two pairs of electrons between atoms; Draw Lewis structure.

13. Learning Check
Draw Lewis structures for SO2 and SO3. Complete each structure by adding the missing valence electrons.

14. Resonance Structures
Occurs in molecules or polyatomic ions with multiple bonds
Are written by changing the location of a double bond 2−

15. 10.2 Shapes of Molecules and Ions (VSEPR Theory)
In the valence shell electron repulsion theory (VSEPR), the three-dimensional shape of a molecule is determined by
Number of electron groups surrounding the central atom
Number of atoms bonded to the central atom
Draw the electron-dot formula
Counting the number of electron groups (one or more electron pairs) around the central atom
Placing the electron groups as far apart as possible around the central atom

16. Two Electron Groups
Central atoms with two electron groups (two double bonds) such as CO2 have a
linear electron-group geometry
linear shape with a bond angle of 180° to minimize repulsion

17. Trigonal planar electron-group geometry
Three Electron Groups
Central atoms with three electron groups (two single bonds, one double bond) such as H2CO have a
Trigonal planar electron-group geometry
Trigonal planar shape with a bond angle of 120° to minimize repulsion H : ..
C O H

18. Three Electron Groups
Central atoms with three electron groups (a single bond, double bond, lone pair) such as SO2 have a
Trigonal planar electron-group geometry
Bent shape with a bond angle of 120° to minimize repulsion

19. Tetrahedral electron-group geometry
Four Electron Groups
Central atoms with four electron groups (four single bonds) such as CH4 have a
Tetrahedral electron-group geometry
Tetrahedral shape with a bond angle of 109° to minimize repulsion
The carbon-hydrogen dash indicates the bond is behind the plane of the paper,
and the wedge indicates the carbon-hydrogen bond is in front of the paper plane.

20. Tetrahedral electron-group geometry
Four Electron Groups
Central atoms with four electron groups (three single bonds, one lone pair) such as NH3 have a
Tetrahedral electron-group geometry
Trigonal pyramidal shape with a bond angle of 109° to minimize repulsion
The wedge-dash notation represents the three-dimensional shape of the molecule.

21. Tetrahedral electron-group geometry
Four Electron Groups
Central atoms with four electron groups (two single bonds, two lone pairs) such as H2O have a
Tetrahedral electron-group geometry
Bent shape with a bond angle of 109° to minimize repulsion
The wedge-dash notation represents the three-dimensional shape of the molecule.

22. Molecular Shapes

23. Molecular Shapes

24. Learning Check
State the number of electron groups, lone pairs, and bonded atoms, and use VSEPR theory to determine the shape of the following molecules:
(1) Tetrahedral (2) Trigonal pyramidal (3) Bent
PF3 B. H2S
CCl4 D. PO43–

25. Solution
State the number of electron groups, lone pairs, and bonded atoms, and use VSEPR theory to determine the shape of the following molecules:
tetrahedral (2) trigonal pyramidal (3) bent
PF3 4 electron groups, 3 bonded atoms, lone pair, trigonal pyramidal (2)
H2S 4 electron groups, 2 bonded atoms, lone pairs, bent (3)

26. Solution
State the number of electron groups, lone pairs, and bonded atoms, and use VSEPR theory to determine the shape of the following molecules:
tetrahedral (2) trigonal pyramidal (3) bent
CCl4 4 electron groups, 4 bonded atoms, lone pairs, tetrahedral (1)
PO43– electron groups, 4 bonded atoms, lone pairs, tetrahedral (1)

27. 10.3 Electronegativity and Polarity
We can learn more about the chemistry of compounds by understanding how electrons are shared in bonds.
Bonds formed by identical atoms share the bonding electrons equally.
Bonds formed between different atoms share the bonding electrons unequally.
Electronegativity
is the relative ability of atoms to attract shared electrons
is higher for nonmetals; fluorine has the highest with a value of 4.0
is lower for metals; cesium and francium have the lowest value of 0.7

28. Electronegativity
Figure The electronegativity values of the representative elements in Group 1A (1) to Group 7A (17), which indicate the ability of atoms to attract shared electrons, increase going across a period from left to right and decrease going down a group.

29. Learning Check
Using the periodic table, predict the order of increasing electronegativity for the elements O, P, and S. O > S > P

30. Polarity of Covalent Bonds
Two types of covalent bonds occur in molecules:
Polar covalent bonds; bonding electrons are shared unequally
Nonpolar covalent bonds; bonding electrons are shared equally
Example: Assign the polarity of the bonds:
C-O N-O Cl-F

31. Learning Check
Complete the following table for each of the bonds indicated.

32. Polarity of Molecules—Nonpolar
In a nonpolar molecule, all the bonds are nonpolar, or the polar bonds (dipoles) cancel each other out. Molecules such as H2, Cl2 and CH4 are nonpolar because they contain only nonpolar bonds.

33. Polarity of Molecules—Nonpolar
A nonpolar molecule also occurs when polar bonds (dipoles) cancel each other because of a symmetrical arrangement. Molecules such as CO2 and CCl4 contain polar bonds with dipoles that cancel each other out.

34. Polarity of Molecules—Polar
A polar molecule occurs when the dipoles from individual bonds do not cancel each other out. For molecules with two or more electron groups, the shape (such as bent or trigonal pyrimidal) determines whether or not the dipoles cancel.

35. Polarity of Molecules—Polar
Examples of polar molecules include HCl, H2O, and NH3.
HCl is linear and contains a polar bond.
H2O is bent and contains two polar bonds as well as two lone pairs on oxygen.

36. Polarity of Molecules—Polar
NH3 is trigonal pyrimidal, and contains three polar bonds and a lone pair on nitrogen.

37. Learning Check
Determine if the molecule OF2 is polar or nonpolar.

38. 10.4 Attractive Forces in Compounds
Attractive forces between molecules and ions hold them close together in liquids and solids.
Solids melt, and liquids boil when the attractive forces between molecules are broken.
Attractive forces between molecules can be
dipole−dipole attractions
hydrogen bonding
dispersion forces

39. Dipole-Dipole Attractions
Polar molecules are attracted to each other by dipole-dipole attractions
when the positive end of one dipole is attracted to the negative end of a second dipole
such as the attractive forces between two molecules of H—Cl

40. Hydrogen Bonds
Hydrogen bonds, especially strong dipole-dipole attractions, occur between
polar molecules containing hydrogen atoms bonded to very electronegative atoms such as fluorine (F), nitrogen (N), and oxygen (O)
a hydrogen atom with a partial positive charge attached to N, O, or F and a partial negative charge on N, O, or F

41. Dispersion Forces
Dispersion forces, very weak attractive forces that occur between nonpolar molecules,
occur when movement induces a temporary distortion of the electrons in a molecule, creating a temporary dipole
make it possible for nonpolar molecules to exist as liquids and solids

42. Bonding and Attractive Forces

43. Learning Check
Indicate the major type of molecular interaction such as dipole-dipole attractions, hydrogen bonds, or dispersion forces expected between molecules of:
NF3
dipole-dipole attractions
Cl2
dispersion forces HF
hydrogen bonds

44. Size, Mass, and Boiling Points
As the size and mass of similar types of molecules increase,
The attractive forces between the molecules also increase
There are more electrons available to produce stronger temporary dipoles
These increased attractive forces increase the boiling points of these molecules.

45. Molar Mass and Boiling Points, Alkanes

46. Attractive Forces and Melting Points
The melting point of a substance is related to the strength of the attractive forces between its particles. Molecules with
Weaker dispersion forces have lower melting points; it takes less energy to break the dispersion forces
Stronger dipole-dipole forces, or hydrogen bonds, require more energy to break the forces between them

47. Highest Melting Points
The highest melting points occur in ionic compounds that have very strong attractive forces between positive and negative ions. Ionic compounds require large amounts of energy to break these forces and melt the substance.

48. Melting Points of Selected Substances

49. Chemistry Link to Health
Biological molecules such as proteins have many different functions. They are needed for
Structural components such as cartilage, muscles, hair, and nails
The formation of enzymes to regulate biological reactions
Transport of oxygen in blood and muscles

50. Chemistry Link to Health
Proteins are composed of building blocks called amino acids. Amino acids have a central carbon atom bonded to
An –NH3+ from an amine and a –COO− from a carboxylic acid
An H atom and a side chain called an R group

51. Chemistry Link to Health
Different amino acids have different R groups. The R group on alanine is a –CH3 group.
(a) The ionized form of alanine contains —NH3+, —COO–, H, and a —CH3 group. (b) The structure of alanine represented as a ball-and-stick model.

52. Chemistry Link to Health
Examples of other amino acids with their side chains include:

53. Chemistry Link to Health
In the primary structure of proteins, amino acids are linked by peptide bonds between the amine and the carboxylic acid groups.

54. Chemistry Link to Health
In a higher level structure of proteins, hydrogen bonds are formed to fold the proteins into different shapes, such as an alpha helix.

55. Chemistry Link to Health
Hydrogen bonding in proteins also occurs between the polar side chains on amino acids on the outer surface of the protein, and the –OH and –H of polar water molecules.

56. Learning Check
Identify the compound in each pair that has the higher melting point. Explain. A. NCl3 or NH3 B. HBr or Br2 C. KCl or HCl

57. Solution
Identify the compound in each pair that has the higher melting point. Explain. A. NCl3 or NH3 NH3 has a higher melting point than NCl3 because the hydrogen bonds in NH3 are stronger than the dipole-dipole attractions in NCl3.

58. Solution
Identify the compound in each pair that has the higher melting point. Explain. B. HBr or Br2 HBr would have a higher melting point than Br2 because the dipole-dipole attractions in HBr are stronger than the dispersion forces in Br2.

59. Solution
Identify the compound in each pair that has the higher melting point. Explain. C. KCl or HCl KCl would have a higher melting point than HCl because the ionic bonds in KCl are stronger than the dipole-dipole attractions in HCl.

60. 10.5 Change of State
Matter undergoes a change of state when it is converted from one state to another at a constant temperature.
Figure Changes of state include melting and freezing, boiling and condensation, sublimation and deposition.

61. Melting and Freezing
A substance
changes from a solid to a liquid at its melting point (mp)
changes from a liquid to a solid at its freezing point (fp)
Water has a freezing (melting) point of 0 °C.

62. Evaporation, Boiling, and Condensation
Evaporation occurs when water molecules gain sufficient energy to escape the liquid surface and enter the gas phase.

63. Evaporation, Boiling, and Condensation
At the boiling point, the molecules have enough energy to overcome their attractive forces and become a gas.

64. Evaporation, Boiling, and Condensation
In condensation water vapor is converted to a liquid as the water molecules lose kinetic energy and slow down. Condensation occurs at the same temperature as boiling, but heat is removed.

65. Heating and Cooling Curves
All the changes of state during the heating of a solid can be illustrated using a heating curve.
Heating curves are a graph, with temperature on the vertical axis and addition of heat on the horizontal axis.
Heating curves illustrate a change
of state, using a horizontal line
in temperature of a substance as energy is added or released by a sloped line

66. Heating Curve, H2O
Figure A heating curve diagrams the temperature increases and changes of state as heat is added.

67. Cooling Curve, H2O
The cooling curve is a diagram of the cooling process and the reverse of a heating curve.
A cooling curve for water illustrates the change in temperature and changes of state as heat is removed.

68. Learning Check
A plateau (horizontal line) on a heating curve represents A. a temperature change B. a constant temperature C. a change of state A sloped line on a heating curve represents

69. Solution
A plateau (horizontal line) on a heating curve represents C. a change of state A sloped line on a heating curve represents A. a temperature change

70. Learning Check
Use the cooling curve for H2O to answer each. A. Water condenses at a temperature of (1) 0 °C (2) 50 °C (3) 100 °C B. At a temperature of 0 °C, liquid water (1) freezes (2) melts (3) changes to a gas C. When water freezes, heat is (1) removed (2) added

71. Solution
Use the cooling curve for H2O to answer each. A. Water condenses at a temperature of (3) 100 °C B. At a temperature of 0 °C, liquid water (1) freezes C. When water freezes, heat is (1) removed